Xcode cannot run iOS simulator

sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService

This brought my simulators back to the run menu, allowed me to add more, and my simulators actually now run again. (Xcode 10b6).

Strangely enough, seemed to clear up a system header build problem too.. now my extra system header search directory location works and no compile error indicating it can't find the files and I did not mod the project.